Opaque glass and semiconductive device made therefrom



Dec. 17, 1963 OPAQUE GLASS AND SEMICONDUCTIVE DEVICE MADE THEREFROM R. H. DALTON Filed July 1, 1959 INVENTOR. fiosser 6. fix); 7'o/v Aria/e4 5) United States Patent Ofilice 3,114,863 Patented Dec. 17, 1963 Yorlr Filed .iuly 1, 1959, Ser. No. 824,337 3 Claims. (Cl. SIP-234) This invention relates to an opaque glass which is particularly suitable as a container for semi-conductive crys tals utilized in electronic components such as transistors and diodes.

Many electronic components have been produced by hermetically sealing suitable crystals such as germanium or silicon in glass enclosures to protect the crystals from deterioration by reaction with undesirable constituents of the atmosphere such as water vapor. Heretofore the glass utilized has been clear glass selected on the basis of favorable expansion properties to allow electrical leads to pass therethrough and with sufiicient electrical resistivity to prevent shorting of the components. The glass enclosed units have then been coated with a dense black paint to prevent change in the characteristics of the crystal which results from its exposure to electromagnetic energy having wave lengths between 0.2-2.0 microns, that is, from the ultraviolet region through the visible spectrum into the region of the near-infra-red. Although it is readily appreciated that an opaque glass would eliminate the time-consuming and expensive operation of painting the finished component as well as producing a coating which would not be subject to chipping or a rasion, it was not believed to be possible to produce a glass which was suitable in all other respects and still have the intense opacity required to absorb the detrimental radiations even in the very thin sections desired.

An object of this invention is to provide a glass which, in sections as thin as 0.5 millimeter and even less, is substantially opaque to radiations between 0.2 and 2.0 microns, has an electrical resistivity greater than 100,000 ohms/cm. at 350 C. and greater than 3,000,000 ohms/ cm. at 250 C., an expansion coefficient of 45 to 55 10 C. between C. and 300 C., an equivalent setting point between 420 C. and 490 C., and a viscosity of at least 15,000 poises at its liquidus to permit drawing of tubing on automatic machines.

Another object of this invention is to provide a suitable glass-to-metal seal between an opaque glass and a netal having an expansion of about 50-60 l0 C. between 0 C. and 300 C., such as molybdenum or ironnickel-cobalt type alloy known in the trade as Kovar.

A still further object of this invention is to provide a semi-conductive device comprising a hermetically sealed, opaque glass container.

Other objects will become apparent to one skilled in the art upon reading the description of the invention as hereinafter set forth and a consideration of the drawing attached hereto.

The drawing illustrates a cross-section View, greatly enlarged of a particularly suitable application for the present invention.

I have found that the above objectives can be achieved in a glass containing by weight 5664% SiO 15-21% B 0 0-4% Na O, 16% K 0, 04.0% Li O, the total Na O+K O+Li O being 4-6%, 25% A1 0 2-10% iron oxide computed as Fe O 0.050.5% sulfur computed as free sulfur and 25% cobalt oxide computed as C0 0 In addition thereto, the glass may contain up to 3% TiQg, and up to 2% V 0 and up to 3% of a re ducing form of carbon computed as free carbon may be added to the batch to increase the intensity of the black color.

be used in combination with sulfur.

The glass-making constituents must be maintained within the above prescribed limits in order to produce all of the necessary requirements in the glass. Thus the alkali and B 0 content must not be less than the indicated minimum in order to produce a meltable glass while more than the stated maximum raises the expansion to an undesirable extent.

The amount of iron oxide, cobalt oxide, and sulfur are critical and each such constituent must be maintained individually and collectively within the stated ranges to produce a usable product. Thus, less than the minimum amount of any of these three constituents results in a glass which does not have the desired opacity throughout the whole spectrum between 0.2 and 2.0 microns. While these constituents have been found to be compatible in a glass melt when present in the specified proportions, exceeding the specified ranges of any one, or more, of these constituents results in the precipitation of metallic cobalt in the glass which makes the glass inhomogeneous and the cobalt will separate from the glass in the melting unit, causing failure of the tank or pot because of rapid refractory attack thereby.

The preferred glass composition as computed from the batch for a crucible melt of this present invention is as follows:

SiO 59.1 B 0 18.3 Na O 1 2 K 0 3 2 Li O 0.8 F3203 8.8 C0304. 3 8 A1 0 2.8 TiO 1.0 V 0 1.0 S 0.4

The stated amounts of the metallic oxides total while the amount of sulfur is given in excess of 100% as, to the extent that it remains in the final glass, it probably is present in anionic form.

The glasses of this invention must be melted under reducing conditions which are achieved by selecting batch materials which are non-oxidizing in character and include suitable materials which are reducing in character. It is apparent from the composition of the final glass which includes sulfur, that elemental sulfur can be included as a reducing agent in the batch. However, iron sulfide, which is an efficient reducing agent, is also a suitable source of sulfur. The iron may be added solely as iron sulfide, but, because of the necessity of maintaining the correct degree of reduction, magnetite is also usually added to the batch in addition to iron sulfide, or iron oxalate, which is another eficient reducing agent, may

Furthermore, additional reducing agent may be added to the batch in the form of carboneous matter such as lampblack, graphite, or powdered coal.

A preferred batch for melting the glass in a 96%-silica crucible in an electrically heated furnace is as follows, in parts by weight:

Pulverized sand 240 Anhydrous borax 21 Anhydrous boric acid 82 Petalite 88 Potassium carbonate 25 Ferrous oxalate 10S Cobalt oxide 20 Titanium dioxide 5 Vanadium pentoxide 5 Sulfur 2 A glass of the preferred composition is produced from this batch in about 16 hours when melted at 1550 C. in a crucible.

The glass so produced has an expansion of 49X 10 C. (-300 C.), an equivalent setting point of 478 C., other physical properties which make it suitable for its intended use and is at least 99.5% opaque to all radiations of wave lengths between 0.2 micron and 2.0 mi crons in a thickness of 18 mils. (Equivalent setting point is a hypothetical temperature utilized in the trade for describing the temperature at which the glass becomes rigid when in sealing relationship to a metal and is further explained in the article entitled Stress in Glass-Metal Seals in lour. Am. Cer. Soc., vol. 3, No. 7, pp. 224 et seq. (July 1950).)

This same batch is not suitable for melting the glass in a pot type furnace as the cobalt oxide is reduced to the molten metal which attacks the pot and causes it to disintegrate. However a suitable batch for melting in a pot is obtained by reducing the amount of sulfur in the above batch to about 01-02%. Thus, while the total sulfur in the batch is thereby lowered, less is lost by volatilization from the pot than from a crucible during the melting process. As sulfur in the sulfide or free sulfur state can be readily oxidized at the elevated temperatures encountered during melting of this glass, the amount of sulfur remaining in the glass is less than the amount calculated from the batch. Likewise, when carbon is introduced into the batch in a reduced state, some of it Will be oxidized to CO which vaporized from the glass melt and hence the amount of carbon remaining in the glass is less than the amount calculated on the basis of the reduced carbon added to the batch.

The glasses of this invention are particularly suitable for the formation of a container for a semi-conductive crystal because they are opaque to radiation having Wave lengths between 0.2 and 2.0 microns. By the term opaque I mean that they transmit less than 1% of the radiation of any particular wave length in the thickness prescribed. Furthermore, these glasses have viscosity characteristics which permit forming the glass into thin walled tubes by conventional tube-drawing apparatus and the glass possesses expansion characteristics and other desirable properties such as setting point, which allows them to be sealed directly to molybdenum or Kovar wire, which is utilized for making electrical contact to the crystal in the container through the walls of the container.

In the drawing, which illustrates in cross-section an hermetically-sealed semiconductive device comprising a a semiconductor element 10, such as a crystal of germanium or silicon, a point contact element 11, a conductor 12 in electrical contact with the point contact element and a second conductor 13 in electrical contact with the semiconductor element. Both conductors, 12 and 13, are molybdenum or Kovar wire. The electricity-carrying elements are hermetically sealed within an opaque glass container comprising an outer glass tube 14 and glass beads 15 and 16, each of said glass elements consisting essentially by weight as calculated from the batch, 56-64% SiO 15-21% B 0 0-4% Na O, 1-6% K 0, 0-1.0% Li O, the total Na O+K O+Li O being 46%, 2-5% A1 0 2-10% iron oxide computed as Fe O 2-5% cobalt oxide computed as C0 0 0.050.5% sulfur determined as free sulfur, 03% Tl02, 0-2% V 0 and 03% of a reducing form of carbon computed as free carbon. The glass beads and 16 are sealed to the conductors 12 and 13, respectively, and each bead is also sealed to the outer glass tube 14.

The preferred method of making the glass-to-metal seal utilizes a bead cut from glass tubing of the specified composition containing a central hole with a diameter slightly greater than the wire diameter. The bead is then slipped on the wire and rapidly heated to a temperature of about 1000" C. to rapidly fuse the bead to the wire. A suitable method of heating the bead is an oxy-hydrogen torch adjusted to a neutral flame.

In making the hermetically sealed semiconductor, one subcombination comprising a bead sealed to a conductor having the point contact element affixed thereto and another comprising a bead sealed to a conductor and to the outer glass tube are preferably assembled prior to the assembly of the complete device. This assembly then re quires only sealing of the glass bead to the outer glass tube in close relationship with the semiconductive element.

What is claimed is:

1. A sealing glass opaque to radiation with Wave lengths of 0.2-2.0 microns and having a coefficient of linear expansion between 0 C. and 300 C. of about to 10" C. suitable for sealing to a wire composed of a metal selected from the group consisting of molybdenum and iron-nickel-cobalt alloy, which glass consists essentially by weight as computed from the batch of 56-64% SiO 15-21% B 0 04% Na O, 16% K 0, 01% Li O, the total NaO+K O+Li O being 46%, 25% A1 0 2l0% iron oxide computed as Fe O 2-5% cobalt oxide computed as C0 0 0.05-0.5% reduced sulfur computed as free sulfur, 0-3% TiO 0-2% V 9 and 0-3% of reduced carbon computed as free carbon.

2. A sealing glass according to claim 1 consisting essentially by weight as computed from the batch of 59% S40 1.2% Na O, 3.2% K 0, 0.8% Li O, 1.0% TiO 1.0% V 0 18.3% B 0 2.8% A1 0 3.8% cobalt oxide computed as C0 0 8.8% iron oxide computed as Fe O and 0.4% reduced sulfur computed as free sulfur.

3. An hermetically sealed semiconductor device comprising a semiconductor element, a point contact element, an outer glass tube, two conductors, each extending through a glass bead and sealed thereto, said first conductor electrically connected with said point contact element, said second conductor electrically connected with said semiconductor element, each of said beads sealed to said outer glass tube, characterized by the fact that each conductor consists of wire composed of a metal selected from the group consisting of molybdenum and iron-nickelcobalt alloy and each glass element consists essentially by weight as computed from the batch of 56-64% SiO 15-21% B 0 0-4% Na O, 1-6% K 0, 0-1.0% Li O, the total Na O+K O+Li O being 46%, 2-5% A1 0 2-10% iron oxide computed as Fe O 25% cobalt oxide computed as C0 0 0.050.5% reduced sulfur computed as free sulfur, 0-3% TiO 0-2% V 0 and 0-3% of reduced carbon computed as free carbon.

References Cited in the file of this patent UNITED STATES PATENTS 756,676 Midgley Apr. 5, 1904 2,220,690 Stupakoif Nov. 5, 1940 2,582,852 Shoemaker Jan. 15, 1952 OTHER REFERENCES Mellor: Treatise on Inorganic and Theoretical Chemistry, vol. 14, page 579.

The Manufacture of Optical Glass and of Optical Systems, 1921, page 100. 

3. AN HERMETICALLY SEALED SEMICONDUCTOR DEVICE COMPRISING A SEMICONDUCTOR ELEMENT, A POINT CONTACT ELELMENT, AN OUTER GLASS TUBE, TWO CONDUCTORS, EACH EXTENDING THROUGH A GLASS BEAD AND SEALED THERETO, SAID FIRST CONDUCTOR ELECTRICALLY CONNECTED WITH SAID POINT CONTACT ELEMENT, SAID SECOND CONDUTOR ELECTRICALLY CONNECTED WITH SAID SEMICONDUCTOR ELEMENT, EACH OF SAID BEADS SEALED TO SAID OUTER GLASS TUBE, CHARACTERIZED BY THE FACT THAT EACH CONDUCTOR CONSISTS OF WIRE COMPOSED OF A METAL SELECTED FROM THE GROUP CONSISTING OF MOLYBDENUM AND IRON-NICKELCOBALT ALLOY AND EACH GLASS ELEMENT CONSISTS ESSENTIALLY BY WEIGHT AS COMPUTED FROM THE BATCH OF 56-64% SIO3, 15-21% B2O3, 0-4% NA2O, 1-6% K2O, 0-1.0% LI2O, THE TOTAL NA2O+K2O+LI2O BEING 4-6%, 2-5% AL2O3, 2-10% IRON OXIDE COMPUTED AS FE2O3, 2-5% COBALT OXIDE COMPUTED AS CO3O4, 0.05% REDUCED SULFUR COMPUTED AS FREE SULFUR, 0-3% TIO2, 0-2% V2O5, AND 0-3% OF REDUCED CARBON COMPUTED AS FREE CARBON. 